Because natural wood is non-recyclable and takes long time to grow, it is always desirable to develop substitute materials, preferably plastic materials, that can take up some of the functions provided by natural wood. However, plastic materials are typically characterized by their inferior flexural strength and flexural modulus, and are thus largely considered non-ideal candidates.
The mechanical characteristics of plastic materials can be improved by combining them with fiber-reinforced materials. In U.S. Pat. No. 3,993,726, the content thereof is incorporated herein by reference, it was disclosed a method of making continuous length articles or reinforced plastic materials. Rovings of temperature resistant material were passed through a crosshead extruder to impregnate the rovings with a thermoplastic polymer under high pressure. The impregnated rovings are pulled from the extruder through a die and are cooled and shaped into a void free article.
In U.S. Pat. No. 4,439,387, the content thereof is incorporated herein by reference, it was disclosed a method of manufacturing a compound composite reinforcing structure, by which a thermoplasitc resin material is bonded to, by mixture with, a composite reinforcing structure. The composite reinforcing structure consists of fibers imbedded in a thermoplastic resin material which is formed by passing extruded plastic resin through a die which imbeds fibers. The compound composite reinforcing structure is formed by mounting a preformed composite reinforcing structure in a molding die and by injecting thermoplastic resin material into the molding die.
In U.S. Pat. No. 4,938,823, the content thereof is incorporated herein by reference, it was disclosed a pultrusion/extrusion method for manufacturing fiber reinforced plastic articles. The method disclosed in the '823 patent involves the step of pultruding a first profile through a die, followed by the step of applying a thermoplastic resin to the first profile to form a second profile bonded integrally to the first profile.
In U.S. Pat. No. 5,277,566, the content thereof is incorporated herein by reference, it was disclosed an extrusion impregnating device for the continuous production of unidirectionally fiber-reinforced polymer moldings with fiber content between 50 and 70 vol-%. The extrusion impregnating device comprises a split casing with a split jacket. The split casing has an extruder connector with a melt inlet for introducing thermoplastic material, a separable impregnating insert with an inlet nozzle for introducing fiber material into the impregnating insert, an outlet nozzle through the fiber-reinforced linear profile exits.
The above mentioned methods have provided certain improvements in the mechanical properties of the finished plastic articles. However, none of them appears to provide the solution for making artificial wood. These methods either provide only one-dimensional reinforcement, do not allow foamed plastics (thus incurring high density), do not allow simple machining (such as nailing, sawing, drilling, etc), or suffer from a combination of these shortcomings.